Paving



Oct. 1s, 1927. 1,645,635

. W. B. WESCOTT PAVI NG Filed Deo. 5, 1925 alf Patent-ed Oct. `18, 1927.

UNITED STATES' PATENT OFFICE.

WILLIAM BURTON WESCOTT, OF QUINCY, HASSACHUSETTS, ASSIGNOB TO THERUI-B- BER LATEX RESEARCH CORPORATION, 0F BOSTON, MASSACHUSETTS, A CORPORA- rIoN or MASSACHUSETTS.

PAVING.

application alea December 5, 1923. serial 1go. 678,673.

This invention relates to paving and processes of producing the same; and it comprises as a new manufacture a paving block or sheet, consisting essentially of rubber and relatively long spun cotton cords or threads-in intimate association, reinforcing means being located in the block or sheet near its lower face, said block or sheetcarrying perforations extending ufrom its upper face to said reinforcing means; and itfurther comprises a paving consisting of said blocks, an underlying foundation, screw or spike means extendmg through the continuous rubber of the lower portion of said block into said foundation, and plugging means above the heads of said screws or spikes; all as more fully hereinafter set forth and as claimed.

For many reasons, rubber compositions form an ideal material forpaving and parqueting purposes, notably for hospitals, steamships, road surfaces, etc., but for practical reasons, they have not been successfully used to more than a limited extent. In a broad way, the lack of success of the various 4propositions which have been made has been due to a failure to appreciate the properties of rubber. Rubber is a practically uncompressible material; and, unlike all other paving materials, it distributes an impressed oad instead of transmitting it directly. In other words, considering a rubber brick used for paving, a load at one point results in distributed stresses at all points within the brick and along its base. For this reason, it is dii'licult to hold a rubber paving in place. For example, if it be kept in place with screws or nails, traffic tends to pull the screws, since a downward thrust at the middle of the brick means an upward pull at other points. Nor can a resilient rubber brick be retained in position by a. cemented union with a foundation at its base.

In the 'present invention, I provide the brick or block with a reinforcement, usually of metal screen or metal netting, located in the lower third of the block. Ordinarily, for paving purposes, I make these blocks about 2 inches thick in the finished state and I find it best' to locate the reinforcementA about half-an-inch from the bottom of the block.

The size of the wire mesh or screen, ofl

. describe 36x18k2 inches, I may employ a heavy `steel wire screenin with a relatively small mesh, such as #8.w1re'with a half-inch mesh. On thls mesh, I apply heavy washers at intervals and then mold the brick in'such amanner as to leave cylindrical holes from the upper surface down to these washers; these holes serving for the subsequent use of' screws or nails passed throu h the washers and screen into a supporting ase below. Ity is convenient to give these l-holes a certain taper. The base may be of Wood, such as pine. Or the base may be of Concrete provided with inset wooden sleepers or plugs. When the base is concrete, without wooden sleepers, I use. bolts of the expansion type. In applying the paving, the screws or nails are put in place andthe holes closed by suitable plugs of the same composition as the body of the block. In making parqueting, which is usually rather thin, I use a liner mesh screen, usually of metal. However,

Woven jute or cotton fabric is applicable .and

may be used in lieu of metal. Parqueting is usually laid in thicknesses ranging from al quarter'of an inch, or perhaps a little less, to ha1faninch. In making par ueting, I proceed in the same way as or ma lng blocks', except that commonly I prefer the more convenient sheet making operations to those used in molding. Parquetry material is thin and with it, it is not necessary or practicable to use 'the relatively heavy anchoring means desirable for the retention of pavin blocks. The deep recesses lor holes in connection with the paving blocks are not usually employed with parquetry strips. 4 p

' As the composition for making these blocks, I desire one of such a resiliency that a steel ball dropped on it will rebound to a height of one-tenth that from which it falls.

ing pav- The resiliency required to meet conditions of 1s, cord or thread, into the composition; say

fiber ranging from half-an-inch to one and a half inches. While it is not practicable to incorporate'fibers of a length. such as this into rubber compositions by the ordinary .milling processes, since milling disintegrates the fibers, yet it can be done by the use of special expediente hereinafter indicated. Long bers can, of course, be frictioned with rubber; or treated with rubber by what are known ,as y rubber solutions, rubber taken up by benzol and the like. But with these methods of bringing rubber and fiber together, there is not the union which I iind desirable for the present purposes. To accomplish my ends, the bonding rubber of the composition must be distributed through the ber; not merely enter its surface irregu larities.

A convenient and cheap source of liber of the character I desire is comminuted tire stock. Such tire stock carries a varying amount of partially cured rubber which has been frictioned on the fabric; there being a greater or less proportion of irregularly shaped pieces of partially cured rubber rang` ing in size from dust particles to pieces just small enough to pass through the sizing screens which are used to return -coarser fragments to the comminuting mills. The size of comminuted tire stock I lind most advantageous is that which will pass through a th inch mesh screen.

In old tires, the averagel ratio of partially cured rubber to cot-ton is about as 1:1 While for my fpurpnses, I desire a somewhat higher ratio o fiber; that is, to meet the requirements of surface coetiicient of friction and a relatively low resiliency, such as the 10 per cent mentioned, there should be somewhat more cotton than occurs in scrap. And I do not desire to use the short fiber, lint, fine particles and dust, such as occur in the pred- ,uct of the comminuting mills in making paving blocks, as these tend to decrease the strength of the finished material.A Therefore, I usually further screen the tire stock to get rid of fines, preferably in a revolving tumbling screen, as this tends -to brush upv the ends of the cut ber cords, so' that each little cord has a shaving brush appearance at the en While fiber and rubber from other sources may be used, com ininuted tire stock, especially when treated as described, is cheap and convenient, and gives particularly good results for my purposes. Scrap from rubber frictioned cotton conveyors and power transmission belting gives much' the same material. The mutual relation of rubber and fiber in tire stock is, for reasons reviously stated, not as good as is desirab e for my purposes; but this I remedy by an expedient.

In a practical embodiment of my process, presuming that 'I am making 2-inc`n paving blocks, 36x18 inches, to be laid on a firm foundation, the dry commnuted and screened tire stock is impregnated with a rubber latex which is advantageously concentrated tocarry about 50 per cent rubber.

This concentration is advantageous over unconcentrated lat-ex, although not necessary, since it cuts down the length of a subsequent drying operation. Latex is a material of freely penetrating properties and it permeates the ber and unites with the rubber, forming in a subsequent operation a unitary body or composition. impregnation is best carried out by the usual vacuum method, though ordinary immersion and churning furnishv a fairly satisfactory product. It is ordinary desirable so to treat the latex as to cause a partial or slight ceagulation to taire place at the time of impregnation. This may be accomplished by partially neutraliz-A ing the ammonia which is usually present as a preservative; a suitable acid being added in such amount as to cause merely a slight thickening of the latex mass. In'so doing, While there is some agglomeration of. caoutchouc particles, a large proportion of the caoutchouc particles will remain in their normal .latex state and are capable of entering the interstices of the tightly twisted cords of the tire scrap. Such a limited co agulation at this stage facilitates subsequent manufacture, since the molded mass is easier to remove as a whole from compression and drainage molds Without crumbling or disintegration. 'lie mass containing the latex is placed in a suitable mold having foraminous Walls. In the present instance, making a Q-inch block, I fill the mold with the mass to a height of one-half an inch and then insert the reinforcing Wire screen. On the screen at the desired places are located metal washers and above each of these washers and' holding it in place is a conical mold piece. The mold is then completely filled with theylateX-Wet mass. Before putting this mass in the mold, there is incorporated into it such vulcanization agent. as may be subsequently necessary. The' amount of vulcani'zation agent may be the same in the `first portion of the mass put into the mold, which forms the :base ofthe brick, as in the second portion added, which forms the u per portion, or it may be dilerent. Or narily, I iind that a simple addition of about 5 per cent of sulphur (on the rubber in the latex) is sufficient to give the best cure in Subsequent treatment. Themass in the mold is compressedV to a deiinite volume, excess of watery liquid .being expelled. By so doing, I obtain for a given quantity of tire stock a definite latex addition. In general, not less than 10 nor more than i5 er cent latex rubber is required to satisfy t e cottom cord interstices and thoroughly bond the mass.

In general, because of the -after-curin and ageing effect of the proteids containe in raw latex, I believe it advantageous tol purify the latex somewhat,`freeing it to la greater or less extent of its non-rubber con- The more nearly the latex approaches a watery emulsion of relatively pure rubber derived from normal latex, the better. Concentraticn and purification may be eected by a particular treatment and washlng 1n a centrifugal, as more fully described and claimed in m copending application, Serial lso ed November 18, 1922. In making parqueting, where a lower compressive strength is adequate, the screened' out portions of tirestock not usedfor pav-v ing stock, short lengths of cord, lint, rubber dust, etc., may be used. Sometimes, for light duty, in`l oiices, hospitals and the like, no special metal or other reinforcement may be required. But for heavy duty purposes, such as factory floorings and the like, the rein` forcement is.` advantageous, as tending to reduce buckling under load.

Returning to the example, after the block has been formed and shaped under pressure, it is transferred to suitable drying means, such as a vacuum drier of the shelf type. At

this time, the brick blanks are relatively soft.

and contain a considerable amount of water.

This is removed in the drier, leaving a high- Ily resilient, porous, sponge-like, but very tough mass. `Advantageously, in the drying, the moisture is reduced to 1 per cent, or lower. Rubber does not satisfactorily adhere to dam liber. in a suitable mold and vulcanized. I lind it desirable" to carry out vulcanization under rather higher pressures than are commonly employed in the ordinary curing of rubber articles. For paving material carrying the cotton cord or thread, in general I find long it esirable to have a pressure not less than 1000 pounds-l per square inch. In curing parquetry material, pressures of this order of magnitude lare generally also desirable; but

f it is. sometimes expedient, for various reav the same composition, wet wit sons, to use lower, pressures, say, pressures of y500 pounds or thereabouts. Vulcanization may be accelerated in the usual way, by the use of accelerators in lconnection with the sulfur. A

In using the finished block, I ordinarily apply it to a wooden foundation which may be of pine boards, laying the bricks in a selfcuring rubber cement. Spikes of the drive screw type are driven down through the holes passing through the washers and the screen and the lower quarter of the material into the underlying wood. I ordinarily yaim lto use these spikes in such a way as to comress the lower half-inch (in a two-inch 1ock)"of rubber by about 10 per cent. This insures a constant upward pull on the drive screw and tends to prevent the loosening of these retaining means by vibration. I then close the holes', usually with ta red plugs of liethe self-cur* in cement and driven home in their pockets. e ordinary, fillers, zinc oxid, Whiting,

The dried blank is placed.

ber and cotton in nearly the relation as that "'10 in whch they exist in old tire stock. -As

stated, I usually lind it better to increase the ratio of cotton to rubber in the scrap somewhat.' Old tire stock, having about l'equal quantities of rubber and cotton, gives 'a brick having a compressive strength comparable to good concrete and a resiliency of about 40 per cent. When the ratio of rubber is reduced to 25 per cent, the resiliency drops to about 10 per cent and the compressive strength goes up to nearly three timesthat of good concrete. i

In the -accompanying illustration, I have shown, moreor less diagramma-tically, various stages in the operation of producing a complete paving block and paving. y

,In Fig. 1, element 1 shows a perforated or foraminous mold of steel or other suitable material. As illustrated, it contains the first or bottom layer of latex-wet material 2 with .block of paving material. As yhere shown, it

is'provided with four orifices 7 in the upper portions for receiving screws or spikes to attach it to a foundation. The View shows a complete block rea'dy for laying. While as shown it has lourpolnts of attachment,'there may be more or fewer. y

In Fig.4 is shown, fragmentarily, the block in position. In the left hand frafrmentary view the block is shown attached to a wooden. foundation 8 by meanskk of' drive screws 9 passing through orifices 7 and seated on the washer described. In the right hand portion of the view, the showing is the same,

ksave that the space above the drive screw vao dation 8. Rubber cement may also be used I between the contacting lateral faces of the adjacent blocks.

In the present invention, the stri of reinforcing material in the lower thir of the block prevents stresses producing longitudinal stretch of the block as a whole; and it limits the upward pull on retaining` vor the grease dropped from passing automobiles. Because of the firm anchorage, and unlike rubber pavements of other types, the wear on the undersurface is reduced to a minimum, and the pavement will remain in place throughout its effective life. Some.- times,l for special purposes, I incorporate slightly morey sulfur or accelerating agent into the lower third or quarter of the article than into the upper portion; or cure in such a manneras to produce greater hardness on the lower surface. Curing of the lower sur-- face may even go so far as to make it of the. nature of ebonite or hard rubber. In general however, when I do this, for the sake of economy and for other reasons, I may incorporate into the base a little hard rubber,

y as in the form of hard rubber builings. Or

I may use some granular filler here. But for reasons already stated, I do not ordinarily desire filler in the top portion, or wearing portion, of the block. This portion I prefer to be com osed only of rubber and relatively long i er, as I secure the best results in this way. With a paving block made as described, the poor heat conductivity of the upper portion tends to minimize the loosening of the deep-seated drive screws by expansion and contraction, and. the lower half-inch or so of rubber, which the drive screw pierces, being compressed about the screw shank, makes a substantially waterproof joint, protecting the head of the screw and the underlying washer against corrosion. Ordinaril I arrange things so the lower layer of t e brick is compressed by the drive screw about 10 per cent of its normal thickness. This aids in minimizing motion between the blocksl and the foundation, and affords a means of taking up such contraction and expansion of the anchoring bolts, screws or spikes as may occur under temperature changes. Ordinarily, I make my paving bricks with smooth lateralfsides perpendicular to the wearing surface. The bricks may, or may'not, be cemented together with a self-curing cement for the purpose of waterproofing' the joint. The ratio of partially cured old rubber to cotton or, for that matter, the ratio of total rubber to cotton, is

y the most important single factor aiecting resiliency and compressive strength and this ratio may be varied at will to meet any special. requirements. The characteristics of great toughness and relatively low cost per unit weight make the present material suitable for various uses, such as fenders for ferry slips, mattings for use in lightering, that is to say, mattings to receive discharged cargo as it is landed by hoists, or for-'any other purpose where a strong rubber mass of moderate resiliency is required. In laying parqueting, I find it desirable (usually, though not always), to brush up or buff the lower surface of the sheet before applying rubber cement. Otherwise, the parqueting is laid in the. customary way. y

Ordinarily,old rubber used in new articles is further vulcanized; that is, the degree of vulcanization becomes enhanced; that is, the rubber becomes harder. And in the usual practice, the reclaimed rubber is plasticized. In the present invention, however, it is found as amatter of fact, that this greater vulcanization or hardening of the rubber in the tire stock used does not occur. In the nished article, it remains substantially at the stage of vulcanization where it was in the tire. Under the heavy vulcanization pressure here used, there is a thorough bond be- *il tween the latex rubber and the littlefl pieces of cut rubber coming from the tiredglwith as little Ias 5 .per cent sulfur in th/l latex rubber. The whole rubber mass becomes substantially without appreciable hardening of the previously cured rubber, that is, of the old rubber. Without' committing myself to any theory, it is perhaps possible that sulfur from the old tire migrates, under suitable vulcanization conditions, into the new rubber, giving a cured homogeneous product having substantially the same combined sulfur ratio throughout. In the article of, the

integral and homogeneous:

present invention, the old rubber of the" tire scrap is not foreign matter, but is integral with the rubber derived from the latex.

While I have described paving and par-y quetry articles of the invention as applied to a special base or flooring, it is possible tof use a sectional base attached to the block or sheet; as by curing or vulcanizing the block or sheet to a wooden or other slab. In some embodiments of my invention, suchV a basal rigid body may be used in lieu of, or to co-operate with, the contained reinforcing fabric. What I claim is U 1. A paving block or sheet consisting of comminuted tire stock carrying relatively long threads or cords and impregnating' 'latex rubber, said block or sheet carrying' a horizontally placed reinforcement near its lower face and interlocking with said fibers.

2. A paving block or sheet consisting of l comminuted tire stock carrying relatively lnl long threads or cords and impregnating latex rubber, said block or sheet carrying a horizontally placed metalreinforcement near its lower face interlocking with sald fibers and being provided with orifices extending from its upper face to said reinforcing means. y

3. A paving lilock or sheet consist-ing of an assemblage of rubber and cotton fibers' between an inch and an inch and a half in length, part of said rubber being latex rubber, said block or sheet carrying a horizontally placed metal reinforcement near its lower face interlocking with said fibers and being provided with orifices extending from vits upper face to said reinforcing means.

4. As a new paving, a base and rubber paving material attached thereto, said mate- 15 rial having the general composition of tire scrap containing vulcanized rubber and'relatively long threads or cords containing imtained rubber as an integral mass.

5. A paving block comprising a body of relatively long threads of fibrous materiall and vulcanized rubber, and a reinforcing screen disposed adjacent the lower portion of the block in parallel relation to the lower surface thereof, the threads being interlocked with each other and with the screen, and the vulcanized rubber extending as an integral continuous mass throughout the block and interspersed with and surrounding the threads and the screen, the proportion of rubber to fibers being less than 1:1.-

lIn testimony whereof, I have hereunto I affixed m signature.

WI LIAM BURTONWESGOTT. 

